1. Field of the Invention
This invention relates to the field of smoke hoods for removing grease and smoke from the spaces above cooking appliances, particularly in restaurants. It further relates to a method of installing such hoods.
2. Description of Prior Art
The removal of grease and smoke from the cooking fumes passing upwardly from cooking appliances in restaurants or the like is notoriously inefficient and ineffective, particularly if the grease filters are not frequently and properly cleaned. (In the latter connection, it is emphasized that many restaurant employees do not do a sufficiently frequent or adequate job of filter cleaning or maintenance.)
The results of such poor filtering are several, and are serious. For example, the large quantities of grease which pass upwardly from the filters form thick grease coatings on the interior surfaces of chambers and ducts, on the blower parts, and sometimes on the adjacent exterior portions of the restaurant building. The result is an unsanitary mess, which creates a distinct fire hazard. Frequent cleanings are therefore required, and fire insurance rates are increased.
As another example, the grease particles in the air constitute a major factor in "smoke," which is beginning to be proscribed by air pollution laws and regulations. If there were no grease in the exhausting air, there would be relatively little "smoke," and the air pollution regulations would usually be met. There is now on the market apparatus, of the electrostatic-precipitor variety, for removing grease and other particles from the air passing upwardly from a restaurant cooking appliance. Such apparatus is very costly, and requires frequent and difficult cleaning particularly since it rapidly becomes coated with grease.
Prior-art reference is hereby made to my U.S. Pat. No. 3,664,255, issued May 23, 1972 for an Apparatus and Method for Removing Fumes from the Space Above A Cooking Appliance, and also to Pat. No. 3,566,585, issued Mar. 2, 1971, for a Grease-Extracting Apparatus, inventors Mona A. Voloshen and Danny B. Deavor. Elements of these patents form elements of certain embodiments of the present invention, as set forth below.
Another element of all embodiments of the present invention is a greatly extended exhaust or plenum chamber. The exhaust or plenum chambers of prior-art smoke hoods known to applicant were rather small, and/or were disposed entirely in the room wherein the smoke hood was located. Such chambers were connected by ducts (for example, the ducts or conduits 43, FIG. 4, of said U.S. Pat. No. 3,664,255) to the exhaust blower on the roof of the building.
It is generally a building or safety code requirement that the lineal velocities of the exhaust air flowing through such ducts be very high, normally in excess of 1500 feet per minute. To achieve such high lineal velocities, and to simplify the problem of penetrating the ceilings of the restaurant kitchens, the ducts are conventionally quite small in cross-sectional areas and cannot be regarded as extended exhaust or plenum chambers. Applicant has discovered that great benefits are achieved by going contrary to the building or safety codes, in that the exhaust or plenum chamber is greatly extended so that the lineal air velocities are not so high. Such high lineal velocities are normally only achieved, with applicant's apparatus and method, relatively near the exhaust blower.
By employing the greatly extended exhaust or plenum chamber, applicant achieves uniformity relative to air flow across the entire width of the apparatus, and minimization of grease coatings on the various surfaces. (It is emphasized that many grease hoods are ten or twenty feet wide, or wider, and that the air flow must be substantially uniform across the entire width if highly effective filtration is to be achieved.) The relatively uniform drawing or sucking of air through the filters is combined with relatively uniform forced-flow of air against the upstream filter surfaces. It is also, in some embodiments, combined with filters which operate by both impingement and centrifugal action. The result of the combination is a great, surprising removal of grease and smoke, economically and with minimum requirements for filter cleaning and other maintenance. These benefits are added to the benefits emphasized most strongly in U.S. Pat. No. 3,664,255, namely the prevention of waste relative to cooled or heated room air.
Relatively uniform air flow, across the entire width of the apparatus, may be achieved, by the present invention, without following either of the following two approaches (both of which were employed in the prior art): (a) adjusting the filters differently at different points across the width of the apparatus, and (b) placing screens or baffles or the like in the plenum adjacent the filters or in connecting ducts. Approach (a) (which has been employed by prior art workers in conjunction with the filters of the above-cited U.S. Pat. No. 3,566,585) is undesirable in that the adjustment impairs filtration in certain regions. Approach (b) (also in the prior art) is unsatisfactory for reasons including the fact that the screens plug up with grease, and baffles (unless employed in an extended plenum) do not do the job satisfactorily and/or collect grease excessively. Reference is made to the above-cited U.S. Pat. No. 3,664,255 at column 5, lines 24 et. seq., wherein baffles are mentioned.
Relative to another aspect of the prior art, that of installing the hood, this has always (insofar as applicant is aware) been a multi-step operation. The hood is first manufactured at a factory, then moved into the restaurant through a hole in a side wall (which hole must later be filled). Then the hood is lifted up toward the ceiling, and local (highly expensive) sheet metal men install and connect the blowers and ducts. In the case of the present extended-plenum apparatus, such local fabrication and/or installation of the plenums has proved to be a major problem since it tended to be done incorrectly. After installation, it was necessary to perform testing and make adjustments. It is therefore of major importance that the entire apparatus (including extended plenums) by fully manufactured and fully tested at the factory, then installed at the restaurant with no necessity for local sheet metal workers or for a hole in the restaurant side wall.